Method and apparatus for filtering slurries containing solid particles having interlocking tendencies

ABSTRACT

Improvements in a known method and apparatus for filtering slurries containing solid particles that have strong interlocking tendencies, e.g. metallurgical slurries, such as cement copper precipitates, by filter press techniques.

United States Patent [72] Inventor [21 Appl. No. [22] Filed [45]Patented [73] Assignee Arthur M. Moler Salt Lake City, Utah Feb. 10,1969 Mar. 2, 1971 Kennecott Copper Corporation New York City, N.Y.

[54] METHOD AND APPARATUS FOR FILTERING SLURRIES CONTAINING SOLIDPARTICLES HAVING INTERLOCKING TENDENCIES Primary ExaminerReuben FriedmanAssistant Examiner-C. M. DiHow Attorneys-John L. Sniado and Mallinckrodtand Mallinckrodt, P. H. Mallinckrodt and Philip A. MallinckrodtABSTRACT: Improvements in a known method and apparatus for filteringslurries containing solid particles that have strong interlockingtendencies, eg. metallurgical slurries, such as cement copperprecipitates, by filter press techniques.

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23 C 23 C Z3 27 Z8 7 Z8 29 30 29 3Q PATENTEUHAR 21% 35673018 ATTORNEYSMisses Ann APPARATUS son rrtrsninc swamps CUNTMNWG sotm rnarictss nxvrnoinrrntocirmc 'rrnnnncnss BACKGROUND OF THE INVENTION l. Field Theinvention is in the art of filter presses adapted to filter slurriesunder pressure to separate liquid and solid phases.

2. State of the Art Filter presses for the filtering of a variety oftypes of slurries have been known and used for many years. Thesetypically include an elongate structural framework, in and along whichare mounted a series of plates that define a corresponding series offilter chambers for receiving, under pressure, a slurry to be filtered.Filter media, usually in the form of a filter screen or cloth or bothstretched over a channelled support, are positioned at opposite sides ofeach plate for receiving and conducting away the liquid phase of theslurry, while rejecting the solid phase. The residue solids collect inthe filter chambers between the plates and form relatively dry cakes.These are discharged when-the press is opened bysslicling the platesapart along the frame. Air pressure applied in reverse through thefilter means may be employed to dislodge the filter cakes, or to dry theresidue solids constituting the cake.

There have been limitations on the types of slurry that could besuccessfully handled by such presses, even with special arrangementssuch as conveying screws and vibrating bars for keeping flow passagesopen. Thus, so far as applicants are aware, there have never beensuccessful commercial installations of filter presses for the handlingofsuch difficult slurries as those containing cement copper precipitatesthat result from precipitating copper on metallic iron from solutionsobtained by leaching copper ores, for example, in accordance withwell-known procedures. The particles of precipitate copper have stronginterlocking tendencies. Recent attempts to filter, by use of acommercial filter press, a slurry of precipitate copper derived from alargedump-leaching operation at an important copper mine wereunsuccessful because of plate deformations due to localized excessivepressures within the press. Recommendations by the manufacturer of thepress did not correct the difficulty.

SUMMARY OF THE DISCLOSURE in accordance with the invention, it was foundthat the difficulty was due to random plugging of slurry feed passagesleading to the filter chatnbers, resulting in localized areas of greatlyexcessive pressure that warped the plates and destroyedthe usefulness ofthe filter press until the warped plates were replaced. it was only whenthe normal size of the slurry feed passages was increased sufficientlyto prevent buildup of the solid particles phase of the slurry acrosssuch feed passages, that the problem was solvedlt was found that thiscould be done without unduly reducing the filtering rate or increasingcake thickness to unwieldy proportions.

Filter presses can be either of recessed plate type or of flush plateand frame type, depending upon whether the plates are recessed todefine, with adjoining plates, filter chambers at opposite sidesthereof, or whether frames are interposed between adjoining flat platesto form the filter chambers. The invention is applicable to either typeof filter press.

The manner in which the size of the slurry feed passages is increased inaccordance with this invention is dependent upon the particularconstruction of the filter press in any given instance. ln the filterpress of the Augerot US. Pat. No. 3,347,383, which is a typicalcommercial type utilizing recessed plates of square or rectangularconfiguration, it is presently preferred to increase the size of theslurry feed passages by interposing an appropriately thick, sealingframe of polyurethane or like material between each set of adjoiningrecessed plates. However, there are a variety of other ways in which thedesired increase in size can be attained, for exampie, by increasing thedepth of the recesses in a customary recessed plate filter press andutilizing the customary packing material to seal the joinders betweenadjoining plates.

THE DRAWINGS In the accompanying drawing, which illustrates a filterpress construction presently contemplated as the best mode of carryingout the invention in actual practice:

, FIG. l is a schematic view in front elevation of an Augerot type offilter press as it appears in closed condition during a filteringoperation;

FIG. 2, a transverse vertical section taken on the line 2-2 of FIG. 1and drawn to a considerably larger scale to show, in full faceelevation, an individual filter plate of the press as conventionallyformed; and

FIG. 3, a fragmentary longitudinal section taken on the line 33of FIG. 2to show the frame elements added to the conventional filter plates toincrease the size of the slurry inflow passages in accordance with theinvention.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENT The filter press shownschematically in FIG. l includes a fixed headI-l mounted on a supportingstructural framework 5 which carries a series of recessed plates P inmutually confronting, adjoining relationship along its length, separatedonly by a corresponding series of special sealing framesF. When thepress is closed during the filtering of a slurry introduced throughinlet pipe-I, the plates P and frames F are clamped together by means ofa movable clamping head M which is also carried by the framework 8 andactuated by a hydraulic orpneumatic jack J to maintain the filter platesand sealing frames in face-to-face, leak-proof relationship. Followingany filtering operation, the press is opened by retracting clamping headM and by separating the plates either manually or by use of a knownplate-shifting device.

As illustrated, the filter plates P are of the fabricated constructionshown by Augerot in FlGS. 1-4 of his aforereferred-to US. Pat. No.3,347,383. They could just as well be of the cast construction shown byAugerots FIGS. 5 and 6, or of any other construction known to the art orsuitable for a filter press of the general nature concerned.

A typical filter plate, FIG. 2., includes a rectangular or a squareframe 10 having four rectilinear side pieces ll, l2, l3, and Mformed ofsteel bar or strip or of stainless steel or other corrosion-resistantmetal, the pieces having their corners mitered and welded together to berigid and self-sustaining. Spanning the corners of the plate frame 10are diagonal frame members l5, l6, l7, andllfi, which define inletpassages 19 and 20 and outlet or discharge passages 21 and 22. It willbe seen from FIG. 3 that the diagonals l5 and 16 are of substantiallyless thickness than the frame members ll, 12 and l3, lid to which theyare welded, respectively, at their ends. This is the way in which slurryinflow passages, leading into the respective filter chambers from inletpassages 19 and 20, are conventionally formed in this type of filterpress. The diagonal frame members l7 and lb are of the same thickness asthe frame members ll, M and i2, and. 13 to which they are welded,respectively, at their ends.

The plate frame members 11 to M and diagonal frame members 15 to 18define an octagonal-shaped inner area which is spanned by a partitionplate 23, lFlG. 3, having its edges received in a groove 24 whichextends completely around the inner periphery of the plate frame it soas toposition the partition plate about midway of the thickness of suchplate frame it). Welded or brazed seams 25 and 26 fix the partitionplate rigidly in the plate frame.

On opposite sides of the partition plate are located chao neled members27 and 28 formed, for example, of noncorrosive expanded metal, such asstainless steel, l /ionel metal, or'

the like. Outwardly of the channeled members 27 and 2d are layers offine mesh screen 29 and 3%, also formed of noncorrosive material, suchas stainless steel, Monel metal, or the' 'like.

The screens are held in place in respective receiving grooves 3i and 32by means of spring strips 33 and 34 or other suitable calking means, allas is conventional in filters of this type.

For the purpose of providing slurry inflow passages 35 and of increasedsize over the normal in accordance with the present invention, there arebonded to opposite faces of the plate frame ill) in this embodiment offilter press respective sealing frames F, FlGS. l and 3, which conformto plate frame lllll except for having no counterpart of the relativelythin diagonal frame members l and 16. That is to say, those corners ofthe sealing frames F, that correspond to the corners of the plate Pwhich have the relatively thin diagonal frame members l5 and lb, do nothave diagonal frame members. Thus, the sealing frames F add to the sizesof the respective slurry inflow passages 35 and 3% by amounts equal tothe thickness of the respective sealing frames F. in accordance with theinvention, the combined thicknesses of a pair of the sealing frames F issuch as to increase the size of the corresponding inflow passages by anamount just lmge enough to prevent random plugging and localizedplate-buckling pressures by buildup of solid particles across suchslurry inflow passages.

As conventionally formed, the shortest dimension of a right crosssection taken transversely across stream flow through the slurry inflowpassages, i.e. the distance between mutually confronting diagonal framemembers or of the similar diagonal frame members lid of adjoining filterplates P, is from about 1 to lihinches. it has been found that typicalslurries of copper precipitates cannot be successfully handled becauseof plate deformations occurring during filtering operations.

increasing the distance between the mutually confronting plate framemember 15 and the distance between the mutually confronting plate framemembers 16 to over twice and usually to'about three times theconventional in accordance with this invention, so as to be within therange of from substantially 2% to substantially 3 /zinches, overcomesthe difficulty, without introducing new difficulties. The normalapproach to handling the difficulty would m to reduce this distance inorder to increase the flow velocity and thereby keep the particles inliquid suspension. This was tried, but did not solve the problem.

There are various ways of increasing the distances between adjoiningfilter plates of a filter press to achieve the objectives of thisinvention; for example, the depths of the recesses at opposite faces ofthe filter plates P could be increased by making the frames ll) of suchfilter plates thicker than normal and utilizing the conventional packingmaterial of the Augerot US. Pat. No. 3,347,383 as sealing gaskets.However, it is preferred to increase the distances by utilizing theillustrated sealing frames F. Although individual filter presses of aparticular type, such as the Augerot type mentioned above andspecifically illustrated herein, may differ among themselves in detailsof construction and operation, including size and throughput capacity,the specified shortest dimension of the slurry inflow passagescorresponding to 35 and 36 herein must not be substantially more thanthe lower and upper limits of the range previously indicated if thefilter press is to successfully handle slurries of dendritic copperprecipitates or the like having a pulp density within the normal rangeof 4 to 15 percent solids wherein substantially all particles are nogreater in size than 10 mesh, US. standard screen, and wherein particledistribution is roughly about 50 percent minus 325 mesh and about 50percent plus 325.

A typical filter press of Augerot type designed especially fordewatering copper precipitate slurries has 16, 48 inches X 48 inchesfilter plates P, each 3 inches in overall thickness. Prior to thisinvention the thickness of each of the slurry feed passages (see 35 and36) was l inch. By eliminating the conventional packing material betweenadjoining plates and by bonding frames F of polyurethane havingrespective thicknesses of 1 inch to opposite faces of such filterplates, the thickness of each of such slurry feed passages was increasedto 3 inches, which proved ideal for overcoming the differential pressureand resulting plate-buckling problem. Moreover, filtering capacity wasincreased from 2.0 tons of dewatered precipitate per operative cycle to2.8 tons without interfering with cake removal nor introducing otherdifficulties.

Reverting now to the illustrated filter press, it will be apparent thatwhen a series of filter plates P and sealing frames F are held inface-to-face relation, all of the inlet passages 19 and all of the inletpassages 20 of the series of filter plates will be in alignment and incommunication through the corresponding open corners, see 37, H6. 3, ofthe sealing frames, as well as in communication with the several filterchambers C through slurry inflow passages 35 and 36, respectively. Alsoall of the outlet or discharge passages 2i and all of the outlet ordischarge passages 22 in the series of filter plates P will be inalignment and in communication through the corresponding comer passages,see 39, FlG. 3, of the sealing frames, but none of these outletscommunicate directly with the filter chambers C. The channels of members27 and 28, which receive the liquid filtrate passing through screens 29and 30, communicate with these outlet or discharge passages inconventional manner (not shown) and the filtrate flows through suchpassages, through the movable clamping header M, and to dischargethrough pipe D.

When a slurry of copper precipitates or the like is supplied to theinlet passages l9 and 20 of adjoining filter plates P, it flows throughthe inflow passages 35 and 36 and into the filter chambers C withoutdifficulty. The liquid phase of the slurry passes through screens 29 and30 and flows along the channels of members 27 and 28 as filtrate andthus to discharge, leaving the solids on the screens and in the filterchambers C.

When the filter chambers C are filled with residue solids, supply ofslurry through pipe I is discontinued and air may be blown through thefilter cake to remove much of the residual moisture. In the case ofcopper precipitates, this prepares them for charging into the usualreverberatory furnace.

As illustrated, air is blown through the filter cake by way of thechanneled members 27 and 28 and screens 29 and 34). it is supplied toeach filter plate P through a pipe 4f}, P16. 2, that communicatesdirectly with the channels of the members 27 and 28, as by a notch (notshown) in the partition plate 23 at the point of interconnection of suchpipe with the groove 2.4. Supply of air is controlled by a valve 41.

The filter plates P and adherent frames F are moved apart along theframework S of the press to discharge the filter cake.

The overall depth, i.e. thickness, of each filter chamber C will beapproximately 4 inches, resulting in a filter cake that is alsoapproximately 4 inches in thickness and that will split through themiddle when the adjoining filter plate and frame combinations areseparated one from another. Although filter cakes of this thickness willtend to fall from the plate and frame combinations and can be easilyremoved if they dont completely fall free of themselves, increasedthickness could give trouble.

It should be realized that the illustrated embodiment is merely one wayof carrying out the invention within the generic teachings hereof.

lclaim:

l. A method of filtering slurries of solid particles that have stronginterlocking tendencies, comprising feeding into a filter press such aslurry under pressure between spaced, mutually adjacent platesconstructed and arranged to form a corresponding series of filterchambers between adjoining plates and in which are formed respectivecakes of the residue solids following extraction of moisture by passageof such moisture through filtering means adjacent to said plates andthrough outlet passages; and maintaining the respective sizes of thefeed streams of said slurry through slurry inflow passages just largeenough to prevent random plugging and localized platebuckling pressuresby buildup of solid particles across said streams, the shortestdimension of a right section taken across each such feed stream beingwithin the range of from about 3.00 to 3.50 inches.

2. A method according to claim 1, wherein the specified shortestdimension is substantially 3 inches.

3. A method according to claim 1, wherein the slurry has a pulp densitywithin the range of 4 to l5 percent solids, and wherein said solidsconsist essentially of particles of dendritic precipitate copper nogreater in size than mesh and distributed roughly about 50 percent minus325 mesh and 50 percent plus 325 mesh.

4. The combination with a filter press, that includes a supportingframework, a series of filter plates constructed and arranged to form acorresponding series of filter chambers between adjoining plates for thereception of a slurry to be filtered and for the collection of residuesolids remaining after the extraction of the liquid phase of thereceived slurry and also arranged to provide slurry inflow passages andfiltrate outflow passages leading, respectively, into and from therespective chambers, of means for sizing the respective slurry inflowpassages just large enough to prevent random plugging and localizedplate-buckling pressures by buildup of solid particles across saidpassages, said means comprising structure associated with adjoiningfilter plates for adding to the normal thicknesses of said filter platessufficiently to made the shortest dimension of a right section takentransversely across the slurry inflow passages formed thereby in theclosed condition of the filter press within the range of from about 3.00to 3.50 inches.

5. A combination in accordance with claim 4, wherein the structure makesthe specified shortest dimension substantially 3 inches. I

6. A combination in accordance with claim 4, wherein the thicknesses ofrespective filter chambers in the closed conditions of the filter pressare approximately 4 inches.

2. A method according to claim 1, wherein the specified shortestdimension is substantially 3 inches.
 3. A method according to claim 1,wherein the slurry has a pulp density within the range of 4 to 15percent solids, and wherein said solids consist essentially of particlesof dendritic precipitate copper no greater in size than 10 mesh anddistributed roughly about 50 percent minus 325 mesh and 50 percent plus325 mesh.
 4. The combination with a filter press, that includes asupporting framework, a series of filter plates constructed and arrangedto form a corresponding series of filter chambers between adjoiningplates for the reception of a slurry to be filtered and for thecollection of residue solids remaining after the extraction of theliquid phase of the received slurry and also arranged to provide slurryinflow passages and filtrate outflow passages leading, respectively,into and from the respective chambers, of means for sizing therespective slurry inflow passages just large enough to prevent randomplugging and localized plate-buckling pressures by buildup of solidparticles across said passages, said means comprising structureassociated with adjoining filter plates for adding to the normalthicknesses of said filter plates sufficiently to made the shortestdimension of a right section taken transversely across the slurry inflowpassages formed thereby in the closed condition of the filter presswithin the range of from about 3.00 to 3.50 inches.
 5. A combination inaccordance with claim 4, wherein the structure makes the specifiedshortest dimension substantially 3 inches.
 6. A combination inaccordance with claim 4, wherein the thicknesses of respective filterchambers in the closed conditions of the filter press are approximately4 inches.